In conventional glasshouse methods, cuttings are rooted in a substrate by holding them in a horizontal plane beneath artificial and/or natural light. As will as requiring a relatively large ground area for each plant, the use of overhead light sources leads to an uneven intensity in the light levels received by individual plants in the crop, and thus growth rates are non-uniform. Working or harvesting the crop from ground level is also labour-intensive and slow due to the inconvenient working attitude.
In U.S. Pat. No. 3,529,379, there is described an apparatus wherein potted plants are placed on trays which are linked to a conveyor system, the plants being maintained in a vertical orientation and passing vertically by a plurality of light sources arranged in a vertical planar array. The plants passing the light sources receive the majority of their incident radiation from the side, rather than in a vertically downward direction relative to the plants.
In U.S. Pat. No. 3,882,634, an apparatus intended to increase plant yield by effectively removing gravitational influences on such growth is described. The apparatus comprises a plurality of plant supports wherein plants are held, the plant supports and plants being rotated about horizontal axes which are substantially perpendicular to the plant stems.
It is an objective of the present invention to provide an apparatus and system for the cultivation of plants wherein a large number of plants can be grown in a small area, with substantially uniform illumination of all the plants in the crop, and with facilitated ergonomic access to the plants for working the crop.
According to a first aspect of the present invention, an apparatus for the cultivation of plants comprises a pair of substantially rigid rotatable end frames mounted for rotation about a common horizontal axis, a number of elongate plant-supporting elements mounted at their respective ends to the respective end frames and arranged with their longitudinal axes generally parallel, the plant-supporting elements being rotatable about their longitudinal axes relative to the end frames, and wherein the plant-supporting elements are provided with radially extending plant receptacles arranged regularly on their surfaces, characterised in that an elongate horizontal linear source of radiation beneficial to plants, emitting radiation substantially uniformly in all radial directions, is positioned along the axis of rotation of the end frames to expose the surfaces of the plant-supporting elements to a uniform amount of incident radiation from all directions relative to the plant stem direction. The plant-supporting elements are rotatable about their respective individual axes, and are also rotatable about the axis of the radiation source in order to achieve uniform exposure to ambient light. The plant-supporting elements are preferably hollow cylindrical components which support the plants in sockets or grooves for growth in directions substantially perpendicular to the surface of the cylinder. Nutrients may be provided to the interior of the cylinder either as a mist, a spray of droplets, or as a liquid stream.
Preferably, the plant-supporting elements are adjustable in their spacing from the radiation source so as to provide for variation of the intensity of radiation incident upon the plants.
While the array of plant-supporting elements rotates about the central radiation source, it is foreseen that auxiliary radiation sources similar to and parallel to the central radiation source may be provided, either at locations fixed in space or at locations fixed relative to the array of plant-supporting elements. By radiation is meant not only visible light but also infra-red and ultraviolet light, the radiation being monochromatic or composed of multiple frequencies.
When the individual plant-supporting elements are rotated about their axes as well as about the central axis, in a "planetary" type motion, it will be understood that the two speeds of rotation will be arranged so that all plants are evenly exposed to the central illumination source. The speeds of rotation of the individual cylinders, and of the array as a whole may be adjusted to optimize the effect on the growth of the plants--slower rotations to promote lateral growth and branching, and faster rotations tending to maintain apical dominance.
According to a second aspect of the invention, a method of cultivating plants comprises the steps of providing an array of cylindrical plant-supporting elements rotatable about a horizontal axis and illuminated by a linear source of illuminating radiation extending along the axis and emitting radiation radially relative thereto, planting a plurality of plants in plant-receiving sockets and fixing said plant-receiving sockets to said plant-supporting elements, and rotating the array of plants and plant-supporting elements about the linear radiation source to effect a rotation of the plants about horizontal axes, for a predetermined growth period of the plants.
In advantageous developments of the method, cuttings for propagating plants are taken and are placed in plant-receiving means arranged along an elongate planting band and the band is subsequently wound helically about a cylindrical plant-supporting element, with the spacing of the plant receiving means of the band corresponding to the spacing between the sockets of the plant-supporting element or with the band following a helical groove on the cylinder. Two or more bands may be wound about a cylinder, to allow `thinning` of the plants by removing one or more bands from a multiple helix array of bands.